Abstract

The nonvolatile memory thin film transistors(TFTs) using a core/shell CdSe/ZnS quantum dot (QD)-poly(methyl methacrylate) (PMMA) composite layer as the floating gate have been demonstrated, with the device configuration of n+-Si gate/SiO2 insulator/QD-PMMA composite layer/pentacene channel/Au source-drain being proposed. To achieve the QD-PMMA composite layer, a two-step spin coating technique was used to successively deposit QD-PMMA composite and PMMA on the insulator. After the processes, the variation of crystal quality and surface morphology of the subsequent pentacene films characterized by x-ray diffraction spectra and atomic force microscopy was correlated to the two-step spin coating. The crystalline size of pentacene was improved from 147.9 to 165.2 Å, while the degree of structural disorder was decreased from 4.5% to 3.1% after the adoption of this technique. In pentacene-based TFTs, the improvement of the performance was also significant, besides the appearances of strong memory characteristics. The memory behaviors were attributed to the charge storage/discharge effect in QD-PMMA composite layer. Under the programming and erasing operations, programmable memory devices with the memory window (Δ Vth) = 23 V and long retention time were obtained.

Received 22 November 2011Accepted 11 July 2012Published online 15 August 2012

Acknowledgments:

The authors would like to thank the National Science Council and Bureau of Energy, Ministry of Economic Affairs of Taiwan, R.O.C. for the financial support under Contract Nos. 100-2221-E-006-040-MY2, 100-D0204-6, and 100-2221-E-143-005-MY2 and the LED Lighting Research Center of NCKU for the assistance of device characterization.